Note: A 3-degree glide path is typically equivalent to a descent-gradient of 300 ft-per-nm or a 700 ft/mn vertical speed, for a final approach ground speed of 140 kt.
Decelerating on a 3-degree glide path in clean configuration usually is not possible.
When capturing the glide slope with only slats extended (i.e., with no flaps), typically 1000-ft and 3 nm are flown while establishing the landing configuration and stabilizing at the target final approach speed.
Energy Management during Approach
Page 2
AIRBUS INDUSTRIE
Flight Operations Support
Speedbrakes may be used to achieve a faster deceleration, as allowed for the aircraft type.
Usually the use of speedbrakes is not recommended or not permitted when below 1000 ft above airfield elevation and/or in the landing flaps configuration.
Typically, slats should be extended not later than 3 nm before the FAF.
Figure 1 illustrates the aircraft deceleration capability and the maximum possible speed at the OM, based on a conservative deceleration rate of 10 kt per nm on a 3-degree glide path.
The following conditions are considered:
.
IMC (stabilization height 1000 ft above airfield elevation); and,
.
Final approach speed ( V APP ) = 130 kt.
The maximum deceleration achievable between the OM (typically 6.0 nm from the runway threshold) and the stabilization point ( 1000 ft above airfield elevation / 3.0 nm ) is:
10 kt-per-nm x ( 6.0 – 3. 0 ) nm = 30 kt
In order to be stabilized at 130 kt at 1000 above airfield elevation, the maximum speed that can be accepted and maintained down to the OM is therefore:
130 kt + 30 kt = 160 kt
Getting to Grips withApproach-and-Landing Accidents Reduction
MM OM
Deceleration Segment
( 10 kt/nm )
2000 ft
1000 ft
500 ft
0 3.0 6.0 nm
V APP = 130 kt V MAX at OM = 160 kt
Figure 1
Deceleration along Glide Slope - Typical
Whenever being required to maintain a high speed down to the marker, the above quick computation may be considered for assessing the feasibility of the ATC request.
Avoiding the Back Side of the Power Curve
During an unstable approach, the airspeed or the thrust setting often is observed to deviate from the target values:
.
Airspeed is below the target final approach speed ( V APP ); and/or,
.
Thrust is reduced and maintained at idle.
Energy Management during Approach
Page 3
AIRBUS INDUSTRIE Getting to Grips with
Flight Operations Support Approach-and-Landing Accidents Reduction
Thrust-required-to-fly curve:
Figure 2 illustrates the thrust-required-to-fly curve (also referred to as the power curve).
Thrust Required to Fly
3-degree glide slope - Landing configuration
160
150
140
130
120
110
100
90
V APP V minimum thrust
Airspeed ( kt )
Figure 2
Power Curve - Typical
The power curve features the following elements:
.
A point of minimum thrust-required-to-fly;
.
A part located right of this point;
.
A part located left of this point, called the backside of the power curve.
The difference between the available-thrust and the thrust-required-to-fly (i.e., the thrust balance):
.
Represents the climb or acceleration capability (if the available-thrust exceeds the required-thrust); or,
.
Indicates that speed and/or flight path cannot be maintained (if the required-thrust exceeds the available-thrust).
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